Two phase nickel-zinc alloy

ABSTRACT

Process of heat treating and mechanically working nickel-zinc alloys or copper-nickel-zinc alloys produces products having special alpha-beta microstructure characterized by high strength at room temperature and high deformability at elevated temperatures.

Unite w? States Patent Inventors Frank J. Ansuini Suffer-n, N.Y.; JacobSchramm, Spartanburg, SC; Frank A. Badia, Ringwood, NJ. Appl. No.872,314" MH*MW "MW Filed Oct. 30, 1969 Patented Dec. 14, 1971 AssigneeThe International Nickel Company, Inc.

New York, NY.

Original application Oct. 14, 1969, Ser. No. 13,913. Divided and thisapplication Oct. 30, 1969, Ser. No. 872,514

TWO PHASE NICKEL-ZINC ALLOY 9 Claims, 3 Drawing Figs.

US. Cl 148/32, 75/157.5, 75/170, 75/178 Int. Cl C22f 1/08,C22f1/10,C22f1/16 Field of Search 148/115,

12.7, 32,160;75/157.5,l70,178 R, 178C [56] References Cited UNITEDSTATES PATENTS 7 2,101,625 12/1937 Munson 75/157.5 2,101,626 12/1937Munson.... 75/157.5 2,101,087 12/1937 Munson 75/157.5 1,680,045 8/1928Homerberg et al. 148/160 1,680,046 8/1928 Homerberg et a1. 148/1603,005,702 10/1961 Chaudron et a1. 75/1 57.5 3,403,997 10/1968 Badia148/11.5 R 3,046,166 7/1962 Hartmann 148/160 Primary Examiner-L. DewayneRutledge Assistant Examiner-W. W. Stallard Attorney-Maurice L. PinelABSTRACT: Process of heat treating and mechanically working nickel-zincalloys or copper-nickel-zinc alloys produces products having specialalpha-beta microstructure characterized by high strength at roomtemperature and high deformability at elevated temperatures.

PATENIEU mm 4 ml SHEET 1 BF 2 INVENTORY) By W .4, PM

ATTORNEY SHEET 2 BF 2 INVENTORS F g G 3 FRANK JOSEPH ANSUINI JACOBSCHRAMM FRANK ARTHUR BADIA 51 W J ATTORNEY TWO PHASE NICKEL-ZINC ALLOYThe present application is a division of our copending U.S. applicationSer. No. 13,913, filed Oct. 14, 1969.

The present invention relates to metallurgy of alloys in thecopper-nickel-zinc ternary system, including certain nickelzinc alloysat the boundary of the copper-nickel-zinc system, and more particularlyrelates to thermomechanical processing of copper-nickel-zinc alloys andto wrought copper-nickelzinc alloy products.

A variety of copper-nickel-zinc alloys have been known for at leastseveral centuries and have been known to possess various desirablecombinations of malleability, mechanical characteristics (includingstrength and ductility) and general corrosion resistance. Manymetallurgical studies of the copper-nickel-zinc system have beenreported in the art and certain metallurgical phases in this system,e.g., the face-centered cubic alpha and several beta-type phasesincluding body-centered cubic beta and body-centered tetragonal betatypes, are well known. Some of the alloys which have a rich white(silverlike) color are known as nickel silvers or German silvers andboth single-phase alpha nickel silvers and dual phased alpha-beta nickelsilvers are known. While the term nickel silver usually refers to alloyscontaining about 9 percent to about percent or percent nickel it isknown that the alpha and beta phases are also obtained incopper-nickel-zinc alloys with much more nickel, e.g., percent or 60percent nickel, and even in alloys containing about 71 percent nickelalong with about 29 percent zinc in which very little or no copper ispresent.

While known copper-nickel-zinc alloys have been used in many articles,including tableware, medical instruments, scientific measuringinstruments and electric switches, it has long been desirable to obtainimproved combinations of strength and ductility characteristics withthese alloys. It has been known that tensile strength, includingultimate tensile strength and yield strength, can be increased by simplycold working the alloys. However the strength increases obtained by coldworking have been accompanied by serious reductions in ductility,particularly tensile elongation. Furthermore, even when tensile strengthhas been increased by cold working, fatigue strength characteristicshave remained undesirably low. Need for high fatigue strength incombination with a high yield strength or elastic limit has beenparticularly great where the alloy is needed for making vibratoryelements and springs.

Tensile strengths can also be increased by addition of other elements,such as aluminum, titanium or columbium, which enable strengthening byage hardening, but age hardening has not satisfied the need forincreased fatigue strength and the heat treatment requirements cansometimes introduce manufacturing difficulties.

Another important need has been to obtain highly improved fonnability inorder to enable production of a greater variety of shapes in products.Enhanced formability has been especially desirable for increasing theusefulness of the white colored copper-nickel-zinc alloys inasmuch asthe rich silverlike color of these alloys is highly desirable forarticles that are both ornamental and utilitarian, e.g., tableware suchas cream pitchers and gravy boats. It has been very obvious thatimproved formability characteristics would provide artists, craftsmanand engineers with greater scope for designing to meet esthetic andengineering needs.

Although many attempts were made to overcome the foregoing difficultiesand others and provide copper-nickelzinc alloy products having improvedcombinations of strength and ductility characteristics, none, as far aswe are aware, has fully satisfied all of the outstanding needs.

There has now been discovered a thermomechanical process that providesnickel-zinc, including copper-nickelzinc, alloy products with new andenhanced characteristics of strength and ductility, includingformability, along with good corrosion resistance.

An object of the present invention is to provide a wrought and heattreated nickel-zinc (or copper-nickel-zinc) alloy product having atwo-phase microstructure characterized by a useful combination ofstrength, ductility and corrosion resistance.

A further object of the invention is to provide a process for workingand heat treating nickel-zinc alloys to produce strong, ductile andcorrosion resistant products thereof.

Other objects and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawing in which:

FIG. 1 shows an alloy composition diagram pertaining to thecopper-nickel-zinc ternary system;

FIG. 2 is a reproduction of a photomicrograph taken at a magnificationof 1,000 diameters (1,000X) illustrating the etched two-phasemicrostructure of an embodiment of the wrought and heat treated productof the invention; and

FIG. 3 is a reproduction of a photomicrograph taken at 500xmagnification illustrating the etched two-phase microstructure ofanother embodiment of the wrought and heat treated product of theinvention. The microstructure illustrated by FIG. 2 and FIG. 3 were bothproduced in accordance with the process of the invention.

Generally speaking, the present invention contemplates a wrought andheat treated product made of a special alloy composition containing zincand nickel, advantageously 8 percent to 40 percent nickel, and in mostinstances copper, and having a two-phase microstructure comprising afine grained alpha matrix with fine beta particles dispersedintergranularly throughout the alpha matrix. Useful room temperaturecharacteristics of the product of the invention particularly include,among other things, high strength that is generally much greater thanthe normal strengths of conventional copper-nickel-zinc alloys such asnickel silvers, good ductility and formability in combination with thehigh strength, and generally good corrosion resistance. Additionalimportant characteristics obtained with embodiments of the presentproduct include high fatigue strength at room temperature andextraordinarily high formability at elevated temperatures. The inventionalso contemplates a thermomechanical metallurgical process, whichprovides products in accordance with the invention, comprising coldworking an alloy of the special nickel-zinc composition in the alphasolid solution condition (the single phase condition) and then, whilethe alloy possesses strain-energy from the cold work, heat treating thecold-worked single-phase alloy at a temperature at or above therecrystallization temperature and below the alpha/alpha plus beta solvusof the alloy and in the range of about 700 F. to about 1,l50 F. torecrystallize the alloy into a fine-grained structure and simultaneouslyprecipitate fine beta particles in an intergranular dispersionthroughout the alpha matrix. While the product can also have some betawithin the alpha grains, it is to be understood that the beta isdispersed predominately intergranularly.

The special alloy composition of the invention is the range of area ofcomposition in the copper-nickel-zinc ternary system that ischaracterized by an alpha/alpha-plus-beta solvus temperature of 800 F.to l,200 F. Thus, the alloy composition is the area of compositionbounded (including the boundary) by the 800 F. and l,2()0 F. solvuslines and the nickel-zinc (binary) boundary line on thecopper-nickel-zinc ternary diagram; this area of composition inaccordance with the invention is illustrated by the shaded area boundedby the 1,200 F. solvus line ABCD, the nickel-zinc boundary line DE fromabout 29 percent to about 33 percent zinc and the 800 F. solvus lineEFGA. All alloy composition percentages referred to herein are byweight. The coordinates of the points A through G on the ternary diagramin FIG. 1 are set forth in the following coordinate table.

B 8 39 53 C 40 33 27 D 67 33 E 71 29 0 F 29 40 31. G 8 36 56 Animportant area of composition for practical commercial production isbounded by BCFGB.

Where desired, the scope of the shaded area ABCDEFGA which illustratesthe composition of the alloy for the process and product can be usefullydescribed to a straight line approximation with minimum and maximumpercentages as follows:

An advantageous range of composition is included by percentages inaccordance with the following:

Minimum Maximum Nickel: 8% 40% Zinc: %Zn=380.23(%Ni) %Zn==420.23(%Ni)Copper: Balance Balance While the alloy may be referred to as having abalance of copper or zinc, this does not exclude small amounts ofauxiliary elements, such as deoxidizers, desulfurizers, etc., andincidental elements or impurities. Accordingly, the alloy can contain upto about 0.1 percent titanium, up to about 0.03 percent aluminum, up toabout 0.5 percent magnesium and up to about 1 percent manganese. lron,carbon and silicon are undesirable and should be restricted to not morethan about 0.15 percent iron, about 0.05 percent carbon and about 0.05percent silicon and more desirably not more than 0.05 percent, 0.01percent and 0.01 percent of each, respectively. Elements such asbismuth, phosphorus, sulfur and tellurium can be detrimental and shouldbe limited to not more than 0.005 percent each. Although lead is notrequired, up to l percent or higher, e.g., 2 percent lead can be addedto improve machinability. However, where it is desired to obtainespecially good formability at elevated temperatures, lead should becontrolled to low levels such as up to about 0.05 percent oradvantageously not more than 0.015 percent.

In view of the foregoing description pertaining to thealpha/alpha-plus-beta solvus relationships and the shaded area in FIG.3, it is apparent that the nickel, zinc and any copper in the alloy arewithin the ranges of about 4 percent to about 71 percent nickel, about29 percent to about 40 percent zinc and up to about 59 percent copper.

It is also important to note that the controlled composition provides arequired cold workability characteristic that enables cold working thealloy into a condition having a recrystallization temperature below thealpha/alpha-plus-beta solvus temperature, advantageously 50 F. to 200 F.below the solvus, of the alloy.

The alpha component of the microstructure referred to herein is theface-centered cubic structured alpha phase in the copper-nickel-zincsystem and the beta component is one or more of the beta-type phaseswhich have body-centered cubic or body-centered tetragonal structures inthe copper-nickelzinc system. Finely divided alpha-beta microstructuresin accordance with the invention are illustrated (etched with potassiumdichromate) by FIGS. 2 and 3 of the accompanying drawing. FIG Q shsanespecially good fully recrystallized,

balanced two-phase microstructure with equiaxed beta uniformlydistributed in a fine-grained alpha matrix in a product of an alloycontaining about 10 percent nickel, 38.3 percent zinc and essentiallybalance copper (about 51.7 percent copper by difference) which wasprocessed by hot extrusion, solution annealing for 1 hour at l,200 F.and water quenching, thereafter cold rolling to 85 percent reduction,and then recrystallization-precipitation treating for 17 hours at 900 F.followed by air cooling. FIG. 3 shows a marginally acceptable,satisfactory, fine alpha-beta microstructure that is about percentrecrystallized (thus predominantly although not completelyrecrystallized) with some beta not equiaxed in a product which is alsoof an alloy containing about I 0 percent nickel, 38.3 percent zinc andbalance essentially copper and which was processed by hot extrusion,solution annealing for 1 hour at 1,200" F. and water quenching, coldrolling to 72 percent reduction and recrystallization-precipitationtreating for 2 hours at 900 F. followed by air cooling.

The fine alpha-beta microstructure has a fine-grained alpha matrix withaverage grain size diameter not greater than the order of about 10microns. It is advantageous that the alpha grain size be not greaterthan about 5 or 6 microns, such as l to 5 microns, in order to obtainuniformly high strength and ductility characteristics and especiallygood hot formability. The bet particles are generally about the samesize or smaller than the alpha grains. The beta is dispersed at thealpha grain boundaries and, importantly, are in finely divideddiscontinuous pattern and do not form grain boundary networks, films orstringers.

At the start of cold working in the process of the invention, the alloyis in an essentially homogeneous solid-solution condition free fromcoarse structures, such as coarse dendritic or other segregation orprecipitates. Accordingly, where the alloy is prepared by usualprocedures of melting and casting into ingot form, the as-cast structureshould be well broken up by hot working, e.g., extrusion or forging.Moreover, inasmuch as the alloy usually precipitates beta when normallycooled, for instance, when air cooled in section thicknesses of aboutone-half inch or greater, it is important that the alloy be solutiontreated prior to the cold working. Solution treatment to place the alloyin the required solid solution condition can be accomplished by solutionannealing the alloy at a temperature above the solvus (alpha/alpha plusbeta) for a time suffcient to dissolve any second phase and then coolingthe alloy rapidly enough to prevent any diffusion-based reactions, suchas precipitation. Advantageeusly, for solution treatment, the alloy isheated to a temperature of 50 F. to 200 F. above the solvus for about 10minutes to 2 hours and then cooled in the solid solution condition; whenthe alloy contains 4 percent to 8 percent to 20 percent nickel, normalair cooling is sufiiciently rapid for section thicknesses up to one halfinch, but for thicker sections, or when the alloy contains more than 20percent nickel, the alloy should be cooled more rapidly such as by waterquenching. I

With the alloy in the slid solution condition, the alloy is cold workedan amount effective to depress the recrystallization temperature tobelow the solvus, advantageously at least about 50 F. below the solvusand more advantageously 100 F. to about 200 F. below the solvus.Although in some instances as little as 30 percent cold worked (30percent reduction in cross secton area) or possibly less may besatisfactory the alloy is advantageously cold worked at least about 60percent or better, 72 percent or percent, in order to provide sufficientstrain energy for recrystallization into a good fine grained two-phasestructure.

Following the cold working, the alloy while in the cold worked,alpha-phase solid solution condition is subjected to arecrystallization-precipitation treatment by heating the cold workedalloy to, and advantageously, above the recrystallization temperature ofthe alpha phase and yet below the solvus in order to precipitatesufficient beta phase to control the recrystallized alpha grain size.Advantageously, the recrystallization-precipitation treatment is at toabout below the solvus for a period of one-quarter hour to about 24hours. The recrystallized and precipitated structure provided by theinvention has good stability and, accordingly, the heating time may belonger than 24 hours and the cooling rate may be either fast or slow,e.g., air cooling.

For carrying the invention into practice, an especially advantageousprocessing cycle, especially for alloys containing 8 percent to 40percent nickel, is to solution treat the alloy by heating at 1,l50 F. to1,300 F. for 30 minutes to 2 hours and thereafter water quenching, orair cooling if the alloy contains 20 percent or less, e.g., 18 percent,nickel, cold working the solution treated alloy at least about 80percent and then heat treating the cold worked alloy to not higher than50 F. below the solvus and in the range 750 F. to 1,050 F. for 1 hour to24 hours, advantageously at least 24 hours in order to ensure fullrecrystallization.

The invention provides products, which can be produced by the use of theprocess of the invention, having high yield strengths of 60,000 poundsper square inch (p.s.i.) and higher in combination with very goodtoughness and ductility, e.g., tensile elongations of percent orgreater. Yield strengths referred to herein are by the 0.2 percentoffset method unless otherwise noted. Advantageously, the product ismade with about 20 percent to about 40 percent nickel, moreadvantageously, 24 percent to 38 percent nickel, in order to obtain veryhigh yield strengths of 90,000 p.s.i. and higher, e.g., 100,000 or105,000 p.s.i. with 25 percent nickel. in connection with obtaining veryhigh yield strength along with good ductility and other characteristics,e.g., fatigue strength, it is to be understood that the balancedtwo-phase structure is especially advantageous for these objects. Formost practical commercial production purposes and in order to achievegood control of the zinc content, the product is produced with about 8percent to about 40 percent nickel. With less than 8 percent nickel, thetolerance for variation in zinc is very low, only about plus or minus1.2 percent, and such close control may be very difficult in commercialproduction. With more than about 40 percent nickel in the alloy, controlof the zinc content is difficult due to volatilization at the highmelting points of such alloys and special techniques, e.g., powdermetallurgy or pressure melting, may be necessary in order to prepare thealloy.

Within the range of 8 percent to 40 percent nickel and with zinc andcopper in accordance with the solvus relationships and/or the shadedarea on the drawing, the low nickel alloys containing 8 percent to about20 percent nickel are characterized by good tensile and fatiguestrengths, e.g., 65,000 to 90,000 p.s.i. yield strength, while alsobeing soft and highly malleable at normal hot working temperatures, suchas employed in brass mills, and not requiring a rapid quench after loyscontaining at least 33 percent, e.g., 34 percent, to 40 percent nickel,are advantageous from the viewpoint of corrosion resistance and havevery good strengths of the order of 95,000 p.s.i. to 100,000 p.s.i.yield strength. Control of the composition of these high nickel alloysbecomes more difficult as the nickel content approaches 40 percent.

Further advantageous embodiments and advantages will become apparenthereinafter, inter alia, from the following illustrative examples whichare given for the purpose of giving those skilled in the art a betterunderstanding and appreciation of the advantages of the invention.

A number of copper-nickel-zinc alloys, including the alloys referred toas alloy Nos. 1 through 7, having compositions in accordance with theinvention were prepared by air melting electrolytic copper andelectrolytic nickel together and adding zinc pellets, or a zinc-nickelmaster alloy in the higher nickel compositions, with the melt at atemperature a little above the liquidus. When all the zinc was added,the melt temperature was raised to the pouring temperature, about 150 F.above the liquidus, finished with 0.1 percent titanium addition andpoured into ingot molds. Chemical compositions of alloys 1 to 7 are setforth in the following table 1. The ingots of the alloys were hot workedto reduce the cross section size and break up the as-cast structure;alloys 1, 2 and 4 being extruded to 36- inch diameter rod; alloys 5, 6and 7 being extruded to 1.5 inch diameter rod; alloy 3 was forged andhot rolled to z-inch plate. Generally, hot working temperatures wereabout l,400 F. to 1,600 F. with the lower temperatures being used forthe lower nickel contents in order to minimize grain growth. Prior tohot working the alloys were homogenized by soaking about 2 hours to 4hours at 1,500 F. to l,600 F.

Wrought and heat treated alpha-beta microstructured products inaccordance with the invention were prepared from alloys Nos. 1 trough 7by the following processes P-1 and P-ll in accordance with the inventionas follows. In P-l, applied to alloys 1 through 4, the alloy wassolution treated by heating at 1,150 F for 1 hour and water quenching,then cold rolling to 85 percent reduction in area and thereafter heatingthe cold rolled alloy at 900 F. for 24 hours followed by air cooling. Inprocess P-ll, applied to alloys 5, 6 and 7 the alloy was solutiontreated by heating to l,200 F. for 1 hour and water quenching, then coldrolling to 82 percent reduction in area and thereafterrecrystallization-precipitation treating by heating at 1,020 F. for 4hours followed by air cooling. The

resulting products were in the form of 0.080-inch thick rolled strip.Mechanical characteristics of the products produced by processes P-1 andP-ll were confirmed by tests of standard strip tensile specimens with al-inch by /&-inch gauge section and the thus-obtained room temperaturetensile test results are set forth in the following table I.

TABLE I Composition Product characteristics Ni, Cu, Zn, 0.2% Y, UT S,Elong., percent percent percent Process k.s.i. lr.s.1. percent 10. 0 51.7 38. 3 P-I 67. 7 89. 6 3" 14. 7 49. 2 36. 1 P-I 69. 4 94. 2 29 16. 448. 3 36. 3 P-I 81. 5 99. 9 2-1 19.2 46. 8 35. 0 P-I 90. 1 101. 3 21 525. 5 Balancek 34. 4 P-II 105. 5 118. 0 17 6 30. 2 .....do 33.1 P-Il98.1 121. 1 26 7 38.1 do 31.7 13-11 98.2 129.4 28

1 Yield strength at 0.2% ofiset in 1,000 p.s.hunlts. 2 Ultimate tensilestrength in 1,000 p.s.i. units. 3 Tensile elongation in percent.

4 Balance.

5 By difierenee.

B 0.8% Mn and 0.1% Ti added to melt.

lt is to be understood that the strengths of the two-phase products ofthe invention are much greater than the strengths obtained with alloysof corresponding compositions in the solid solution condition. Forinstance, alloys 1 and 7 when in the solid solution condition had 0.2percent yield strengths of 26,400 p.s.i. and 52,000 p.s.i. ultimatetensile strengths of 64,000 p.s.i. and 108,400 p.s.i. and elongations of65 percent and 24 percent, respectively. it is notable that withcompositions having nickel contents of about 30 percent and 37 percent,the ductility of the high strength two-phase products of the invention,as evidenced by tensile elongations, was as good as or better than theductility of the solution-treated alloys of the correspondingcompositions.

Fatigue testing confirmed that the alloy has high fatigue strength thatis substantially enhanced over the fatigue strength of conventionalcopper-nickel-zinc products such as nickel silvers. A fatigue specimenmachined from the strip product of alloy 3 produced by process P-lsuccessfully survived, or ran out, without fracture when subjected tocyclically applied reversed bending stresses of 40,000 p.s.i.

Of further advantage, the product of the invention has been found toexhibit desirable high ratios of the 0.01 percent and the 0.02 percentoffset yield strengths to the 0.2 percent offset yield strength, forexample, 0.01 percent yield:0.2 percent yield ratios of 0.68:1 and0.87:1, and 0.02 percent yield:0.2 percent yield ratios of 0.85:1 and0.96zl, were obtained with alloys 6 and 7, respectively. These resultsare illustrative of high elastic limit characteristics that arebeneficial for springs and other articles subjected to high elasticstrain in use.

The wrought and heat treated two-phase product can be cold worked, ifdesired, to reduce the cross section or change the shape of the productor to further harden the product. A highly useful feature of thetwo-phase product is that the product can be heavily cold worked andthen given a second recrystallization-precipitation heat treatmentwithout causing any serious degradation of tensile characteristics Thefollowing table ll shows tensile characteristics and hardness testresults obtained with strip products made by processing alloy 3 inaccordance with the process of the invention, both without he additionalcold work, and in the fourth instance with a second heat treatment,after the first recrystallizationprecipitation heat treatment.

of microstructures obtained with various processing of alloys 1, 2 and 3are set forth in table III which illustrates many satisfactoryprocedures which provided satisfactory microstructures A, B, C and D,and also illustrates other procedures resulting in unsatisfactorymicrostructures E, F and G, which are to be avoided. In this connection,it is noted that particularly consistently good results were obtainedwhen alloys 1, 2 and 3, containing 10 percent to 20 percent nickel, werecold TABLE III.MICROSTRUCTURES Heat treatment in cold worked conditionTemperature 700 F. 800 F. 000 F.

Percent Hours cold worked 2 6 24 2 6 24 2 6 24 Allo i 72 G G G G C G C AA l--. 85 A A A A A A A A A 1--. 96 A A A A A A A A A 2--. 86 F G E E AA E B A 2-.. 06 F G A A A A A A A 3--- 72 E E D 3-.- 85 F F G F E A D BA 96 F G E E A A A A A Note: Percent work=Percent reduction incross-sectional area by cold working.

A=Very good-Balanced twohose microstrueture; alpha ully recrystallized;coring minlma or nonexistent; beta lrnely drvlded equiaxed and uniformlyintergranularly distributed throughout alpha matrix. I

B=SatisfactoryTwo-phaso rnlcrostruct-ure; alpha fully recrystallized;minor coring apparent by moderate beta concentration.

C=Marglnally satlsfactory'lwo-phase mierostructure; about 80% alpharecrystallized; some bets. not squeezed.

D=Marginally satisfactoryelpha fully recrystallized but beta notcompletely equiaxed.

E =Not satisfactory-alpha fully recrystallized; substantial beta-freecored areas.

F=Not satisiaotoryalpha not recrystallized; beta on slip lines and ongrain boundaries.

G=Not satls[actory-elphe not recrystallized; heavy beta concentretlon onslip lines and on grain boundenes. f l l ot examined.

TABlTE n 0.2% Y UTS Elong. Herd. Process k.s.i 1 k.s.i.' percent 3 R30T4 ST plus 80% CR plus RPHT 81. l 107. 9 18 7 ST plus 80% CR plus RPHTplus 20% CR. 116. l 131. 1 5 84 ST plus 80% CR plus RPHT plus CR 119. l145. 2 3 35 ST plus 50% CR plus RPH'I plus 70% CR plus RPHT A 79. 6 99.8 24 79 1 Solution treatment at 1,l50 F. for 1 hour and air cool. 1Percent reduction by cold rolling.

5 Recrystallization-precipitation heat treatment at 900 F. for 24 hoursand air cool.

i Rockwell superficial hardness, 30'1 scale,

The two-phase product has also been produced in form of wire bycold-drawing the alloy in the solution-treated condition and thenrecrystallization-precipitation (RP) heat treating the wire; also, theRP heat treated wire has been again drawn and again RP heat treated withgood results, thus confirming the utility of the process formultiple-pass drawing of wire.

The electrical conductivity of the product is of the general order ofthat of commercial nickel silvers of similar nickel levels. Examples ofproducts of the invention containing 10 percent, l5 percent and 20percent nickel had electrical conductivities of 7.9 percent, 6.8 percentand 5.9 percent lACS (international Annealed Copper Standard). it willapparent understood that the conductivity will generally decrease withincreasing nickel. microstructures 800 F.

It is understood that temperatures and times required forrecrystallization are codependent with alloy composition and degree ofcold work. Accordingly, it is understood that the process of theinvention is controlled, within the ranges set forth herein, with regardto alloy composition, degree of cold work and heat treating time andtemperature to result in simultaneous recrystallization andprecipitation. The techniques for the required control are apparent fromthe foregoing examples and other disclosures. As an additional guide tofacilitate controlling the process, the following results worked atleast 85 percent and heat treated at 800 F. to 900 F. for 24 hours;longer heat treatments, e.g., l00 hours or more, would not bedetrimental. it should be further noted that as the nickel is increased,it is beneficial to increase the degree of cold working, the heat treattemperature and/or the heat treat time.

The line alpha-beta structured product of the invention providesextraordinarily high formabiltiy at elevated temperature. For example,an ingot of alloy 3 was hot rolled from 4-inch thickness to Kz-inchplate at l,500 F. The hot rolled plate was solution annealed at l,250 F.for one-half hour, air cooled, then cold rolled at room temperature to0. lO-inch thick strip percent cold work) and thereafterrecrystallizationprecipitation heat treated to 950 F. for 4 hours andair cooled. The product produced by this process of the invention had abalanced two-phase microstructure typical of the microstructureillustrated in FIG. 2 of the drawing. Tensile specimens with a 2-inch byVz-inch gauge portion (01 0-mch thick) were machined from therecrystallization-precrprtation treated strip. Straining such a tensilespecimen of the thus produced product of alloy 3 in tension at aconstant elongation rate starting from an initial strain rate of0.025-mch per inch per minute at 900 F. resulted in neck-free elongationof 305 percent and thus demonstrated that the product had very highformability of a superplastic nature. Moreover, metallurgical inspectionof the product after being elongated over 300 percent showed that nograin growth occurred during the elongation. Another tensile specimen ofthe fine alpha-beta alloy 3 product was likewise, stretched at 900 F.,except that the elongation rate was gradually increased from 0.002 to0.05 inch per minute and resulted in a neck-free elongation of about 300percent without fracture. The unusually high forrnability of the productat elevated temperatures, such as tensile elongation of 200 percent orgreater at temperatures of about 750 F. to about l,000 F., providesspecial utility for hot-forming the product into articles having specialshapes of highly elongated or deep-drawn, or other greatly stretched,configurations by forming methods such as press forging drawing, blow orvacuum forming and others. Furthermore, the hot forrnabilitycharacteristics of the product enable hot-working the product atdesirable low working loads, e.g., low tensilestretehing loads or lowroll-separation forces.

The product has generally good corrosion resistance providing utility infresh water, salt water and other environments. However, the goodcorrosion resistance of the product does not generally extend to coverresistance to stress-corrosion cracking in ammonia and if the product isto be used under stress while in contact with ammonia, the productshould contain at least about 33 percent nickel and advantageously, forprotection against stress-corrosion cracking, should contain 37 percentor more nickel.

The present invention is applicable in the production of strong andductile corrosion-resistant wrought products including sheet, strip,plate, bar, wire and rolled or extruded shapes, e.g., channels,T-sections, etc. Moreover, the invention is particularly applicable inthe production of usefully and/or ornamentally shaped articles,including tableware, e.g., forks, spoons, butter knives, gravy boats,cream pitchers, and other items commonly referred to as holloware, andincluding springs, e.g., barometer springs, diaphragm springs andelectrical contactor springs, musical instrument keys, surgical andmedical instruments, and also costume jewelry. Furthermore, the productis also desirable for use as the underbody of an article cladded withanother metal, especially as an under-body for cladding with silver ascertain of the compositions have a color close to that of silver.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. A wrought metal product having a microstructure consistingessentially of a fine-grained alpha phase matrix and fine beta phaseparticles dispersed discontinuously and intergranu' larly in the alphaphase matrix and composed of an alloy composition selected from thegroup of alloys in the coppernickel-zinc alloy system characterized byan alpha/alpha-plusbeta solvus temperature of about 800 F. to aboutl,200 F.

2. A product as set forth in claim 1 characterized by a room temperatureyield strength of at least about 60,000 pounds per square inch.

3. A product as set forth in claim 1 wherein the average alpha grainsize and the average beta particle size are not greater than about 10microns.

4. A product as set forth in claim 1 composed of an alloy compositionrepresented by a point in the area bounded by the line ABCDEFGA on FIG.1 of the accompanying drawing.

5. A product as set forth in claim 1 composed of an alloy compositionrepresented by a point within the area bounded by the line BCFGB on FIG.1 of the accompanying drawing.

6. A product as set forth in claim 1 comprising at least about 33percent nickel.

7. A product as set forth in claim 1 characterized by a tensileelongation of at least about 200 percent at a temperature in the rangeof about 750 F. to about l,000 F.

8. A product as set forth in claim 1 comprising 8 percent to 40 percentnickel, zinc in an amount not less than the percentage determined by therelationship %Zn=380.23(%Ni) and not greater than the percentagedetermined by the relationship and balance essentially copper.

9. A product as set forth in claim 1 containing lead in an amount up toabout 2 percent.

l R I I

2. A product as set forth in claim 1 characterized by a room temperatureyield strength of at least about 60,000 pounds per square inch.
 3. Aproduct as set forth in claim 1 wherein the average alpha grain size andthe average beta particle size are not greater than about 10 microns. 4.A product as set forth in claim 1 composed of an alloy compositionrepresented by a point in the area bounded by the line ABCDEFGA on FIG.1 of the accompanying drawing.
 5. A product as set forth in claim 1composed of an alloy composition represented by a point within the areabounded by the line BCFGB on FIG. 1 of the accompanying drawing.
 6. Aproduct as set forth in claim 1 comprising at least about 33 percentnickel.
 7. A product as set forth in claim 1 characterIzed by a tensileelongation of at least about 200 percent at a temperature in the rangeof about 750* F. to about 1,000* F.
 8. A product as set forth in claim 1comprising 8 percent to 40 percent nickel, zinc in an amount not lessthan the percentage determined by the relationship %Zn 38-0.23(%Ni) andnot greater than the percentage determined by the relationship %Zn42-0.23(%Ni) and balance essentially copper.
 9. A product as set forthin claim 1 containing lead in an amount up to about 2 percent.